Some managers apparently don't understand that when an employee is taking PTO, they are actually taking time off, away from the office and away from their work responsibilities. If they are not at the office, they do not need to take care of any issues that might come up. There's a reason why companies hire dozens of people in every area. One single human cannot be responsible for everything, and if a person needs to take some time off, someone else should cover for them or manage until they come back.
My dad worked at a big company for over 20 years. He was in charge of a whole department, and he could barely take time for himself. People were constantly blowing up his phone, asking him even the most ridiculous questions, questions that they should have known the answers to, because that was part of their job as well. He sat in front of the computer all day, sending emails, taking care of numbers, knowing where everything was all the time. He would receive a phone call after another nonstop, plus all the meetings. He hardly ever took vacations, and when he did, he might as well have been working remotely, because it was almost the same. He didn't have his computer on, but the phone calls kept coming in from 8am to 6pm. So yes, I've had more than one crazy managers who doesn't respect boundaries and make their employees work even more than they're supposed to.
We all need to set boundaries between us and our work; otherwise, we'll never have time for a private life. And if your managers don't respect your time off, you have carte blanche to go to HR and file as many formal complaints as you need.